LM3406MHEVAL: How to proper connect more parallel LEDs?

Marcin Brylak

Part Number: LM3406MHEVAL
Other Parts Discussed in Thread: LM3550, TPS92515

Dear TI Forum,

I have 2 Eval Boards and 2 LEDs. When I connect LED- from 1st board with LED- from 2nd board then I see current only flowing through one LED and the current is double. That means if I set 700mA and should see 700mA on each LED ( not 1.4A only on one LED). Also what is strange I can measure 0.6V between LED+ and LED- without LED (open circuit), which is strange. Can be that output capacitor storage this voltage? But I can not discharge this capacitor which is also strange. Thanks for any support.

Marcin

over 6 years ago

0 Marcin Brylak over 6 years ago

Prodigy 205 points

0 Clinton Jensen over 6 years ago

TI__Mastermind 25500 points

Hello Marcin,

You should not connect the LED- terminals of the two boards, that is the CS pin of the device so the error amplifiers will fight each other. The grounds of the two EVMs should be connected together then each will regulate current in its LED correctly.

With buck converters you will always see some output voltage with an open circuit. It is still trying to switch because CS is low, but there is nowhere for current to flow. So it will charge the output capacitor to some value. I hope that helps.

Regards,

Clint

0 Marcin Brylak over 6 years ago in reply to Clinton Jensen

Prodigy 205 points

Hello Clint,

Can you please propose an ASIC or Eval Board which can provide ~1.5A for 1 LED and I can control 4 LEDs in parallel? Something similar as shown on the picture above.

Thanks a lot

Marcin

0 Marcin Brylak over 6 years ago in reply to Marcin Brylak

Prodigy 205 points

Hi Clint,
I have found a LM3550 5-A Super-Capacitor Flash LED Driver. Can I used in parallel connection with Iflash 1.5A ?

0 Clinton Jensen over 6 years ago in reply to Marcin Brylak

TI__Mastermind 25500 points

Hello Marcin,

I am not sure about the LM3550 as I have no experience with it. But we have plenty of LED drivers that can do 1.5A. I am just not clear from the picture exactly how you mean to drive the 4 LEDs. Are you connecting them in parallel and using 1.5A (375mA in each LED), or trying to drive 1.5A in each and control them independently? A more clear picture would help as well as what input voltage you have available.

Thanks,

Clint

0 Marcin Brylak over 6 years ago in reply to Clinton Jensen

Prodigy 205 points

Hello Clint,
- 4 LEDs in parallel each 1.5 A
- it can be 1, 2 or 4 LED drivers but with LED to ground ( parallel connection possible)
- yes I want to control them independently
- I need flash led driver
Thanks
Marcin

0 Clinton Jensen over 6 years ago in reply to Marcin Brylak

TI__Mastermind 25500 points

Hello Marcin,

It depends on your input voltage, but you could use one TPS92515 for each LED. It has high-side current sense so the LED cathode can be tied to ground and each can be controlled independently. They are very fast so they will work well for flash applications.

Regards,

Clint

Power management

Power management forum

LM3406MHEVAL: How to proper connect more parallel LEDs?